Bim is a pro-apoptotic member of the Bcl-2 family, that is upregulated in several clinically relevant settings where cell death occurs, including breast cancer cells after chemotherapy, and HIV-1 AIDS. Bim localizes to microtubules, but in response to apoptotic stimuli, it translocates to mitochondrial membranes, where it binds other Bcl-2 proteins and promotes cell death. The mechanisms by which Bim promotes apoptosis are not completely understood, and we propose to address this question with a structure-function correlation strategy that combines the NMR structure determination of Bim, in aqueous and lipid environments, with biological assays. The specific aims of this exploratory research grant application are to: (1) to develop the expression, purification, and NMR sample preparation of Bim; (2) to determine the structure of Bim in aqueous solution and initiate NMR studies for structure determination in lipid environments; and (3) to characterize the biological activity of Bim. The Bim project is in its very early stages, and faces the challenges associated with the structural and functional studies of membrane-bound proteins. The support of a grant from the R21 Program, will enable us to develop the methods and obtain the initial data, that will serve as a platform for additional structural and biological experiments, aimed at understanding the mechanism of apoptosis regulation by Bim in health and disease. The research we propose is multi-disciplinary, and takes advantage of the collaboration between structural (Marassi) and biological (Reed) laboratories, both situated at the Burnham Institute. We have been developing NMR methods for membrane protein structure determination, and their application to Bim and apoptosis is new. If successful, these studies will provide important new insights to mitochondrion-dependent apoptosis, and a potential new therapeutic target for major human diseases.